Doorless telephone booth



March 6, 1956 w. x.. MANNING DOORLESS TELEPHONE BOOTH Filed April 50, 1954 5.5.51. n.: Etui l5 w w/ l United States Patent O r'ice DOORLESS TELEPHGNEBOOTH` Willis L. Manning, Libertyville, Ill., assiguorrto Burgessanning Company, Libertyville, Ill., a corporation of inois Application April 30, 1954, Serial'No. 426,779

3 Claims. (Cl. 2li- 3.5)

This invention relates to acoustically treated, doorless telephone booths.

Booths of this type are known (e. g. Weiss Patent No. 2,141,117, dated December 20, 1938) and have been in general use for many years. While satisfactory in most locations, these booths tend to amplify low frequency components of ambient noise. The sound-absorbing material with which the walls are lined is invariably selectively more effective for the absorption of higher frequencies but are relatively ineffective at frequencies below about 300 cycles per second.

The principal object of the present invention is to provide an acoustically treatedtelephone booth of the doorless type having improved acoustical characteristics in that low frequency noise is not amplified within the booth and may be, to some extent, actually attenuated.

Laboratory investigation has indicated that the low frequency build-up experienced in booths of rectangular cross-section is due to a standing wave pattern which is determined by the interior configuration and dimensions of the booth. The components of the standing pattern include frequencies whose wave lengths are equal to twice the width of the booth, twice the height of the half-size booths illustrated, and four times the distance from the rear wall to the open front of the booth. For booths of practical dimensions, the first two components listed are of sufficiently high frequencies to be within the effective absorption range of available sound-absorbing materials, but the lowest frequency mode, the third component listed, occurs below the region for which acoustical linings are effective. The occurrence of this lowest frequency mode is limited to a relatively narrow frequency band.

It is thus perceived that the doorless telephone booth responds to acoustic excitation from an external source in much the same manner as an organ pipe responds to the driving vibration. It has been found that the troublesome amplification of low frequency noises in these booths may be prevented by providing a low frequency absorber construction in or associated with the rear wall of the booth. This expedient is the basis of the present invention.

The invention will be fully understood by reference to the following detailed description, taken together with the accompanying drawings showing illustrative forms embodying the invention, in which drawings- Fig. l is a perspective View of a half-size or wall type telephone booth incorporating the invention;

Fig. 2 is a cross-sectional view of the booth of Fig. 1;

Fig. 3 is a detail view, in section, taken at the line 3 3 of Fig. 2, and

Fig. 4 is a fragmentary detail View taken at the location indicated by line 4-4 of Fig. 2.

The booth structure illustrated in the drawing incor porates the principal elements of construction of the booth more particularly described in Weiss Patent No. 2,141,117, dated December 20, 1938, in that an outer sheathing comprising side wall elements 27 and a rear wall element 33, together with a top 31 and a bottom wall or shelf 32 2,736,928 iatentecl Mar. 6, 1956 The front is vpermanently open. By way of example of a suitable sound-absorbing construction, the details of the side walls at the line 3-3 are shown in Fig. 3.

woolycellulose orglass fibers, or the like, is arranged interiorly of theside and rear wall elements, a facing 28 of sheet metal, plywood, hardboard, or similar material, perforated to render it sound transparent, being provided to protect and support the sound-absorbing material. if desired, top 3i and shelf 32 may, but need not, be of sound-absorbing construction.

The function of the sound-absorbing walls of the booth is to absorb as large a proportion as possible of the energy of the sound waves incident to the inner surfaces of the both, thus preventing reflection with consequent reverberation and high noise level within the booth. The particular improvement in accordance with the present invention lies in the provision of a combined high and low frequency sound-absorbing system associated with the rear wall of the booth.

To achieve this result, the sound-absorbing construction comprising layer 29 of sound-absorbing material and facing 255 therefor is spaced from rear wall element 33 to form acoustic reactance chambers 30 at the rear corners of the booth. As shown in Fig. 2, the side walls of the acoustic construction converge from the sides of the booth toward the rear thereof in defining the two acoustic chambers. The chambers extend between top 3l and shelf 32.

The sound-absorbing layer 29 and reactance chambers 3) form elements of a combined acoustic system which is effective in the reduction of the sound level within the booth with respect to low frequency sound energy as well as that of the higher frequencies. A major proportion of the low frequency waves pass through the soundabsorbing layer into the chambers wherein their amplitudes are substantially diminished by acoustic interference. The specific improvement factor so far as acoustic performance of the booth is concerned lies in the substantial reduction of the intensity of the troublesome standing wave pattern caused by the reflection of sound waves from the rear and side walls. it is to be noted that since the reactance chambers extend across a substantial part of the side, as well as the rear wall elements, reflection of sound waves by the side, as well as the rear, walls is minimized. rEhe result is increased privacy of conversation and improved message reception for the person using the booth.

It will be understood that other types of sound-absorbing construction may be employed as alternative to the perforated facing-sound-absorbing backing arrangement shown by way of example. This hard surfaced construction is preferable for walls because it is less likely to be mechanically damaged than is, for example, iiberboard or so-called ssured tile without the perforated facing.

invention is claimed as follows:

l. In a doorless telephone booth having side and rear wall elements forming a rectangular partial enclosure and a top therefor and sound absorbing construction associated with said wall elements comprising a layer of sound absorbing material arranged interiorly of said wall elements, the improvement wherein said layer of sound absorbing material is spaced from said side wall elements and from said rear wall element to form low frequency sound absorbing chamber means acoustically coupled with the booth enclosure.

2. in a doorless telephone booth having side and rear Wall elements forming a rectangular partial enclosure and a top therefor and sound absorbing construction asso- A layerv 29 of a suitable `sound-absorbing material, suchas `rock 3 i ciated with said wall elements comprising a layer of sound absorbing material arranged interiorly of said Wall elements and a perforated facing therefor, the improvement wherein said layer of sound absorbing material and perforated facing therefor converge from the sides of said booth toward the rear thereof to form low frequency sound absorbing chamber means between said layer of sound absorbing material and the side and rear Wall elements of said booth, said chamber means being acoustically coupled with the space Within the booth enclosure through the sound absorbing construction.

3. In a doorless telephone booth having side and rear Wall elements forming a rectangular partial enclosure and a top therefor and sound absorbing construction associated with said wall elements comprising a layer of sound absorbing material arranged interiorly of said wall elements and a perforated facing therefor, the improvement wherein said layer of sound absorbing material and perforated facing therefor extend diagonally from the forward part of said side wall elements to the central part of said rear wall element to form two low frequency sound-absorbing chambers between said layer of soundabsorbing material and the side and rear wall elements of said booth, said chambers each being acoustically coupled with the space within the booth enclosure through the sound absorbing construction.

References Cited inthe tile of this patent UNITED STATES PATENTS 704,987 Tufts July 15, 1902 1,043,055 Carter Oct. 29, 1912 2,141,117 Weiss Dec. 20, 1938 2,397,609 Leadbetter Apr. 2, 1946 

